Add Precache.Fetch.MinWeight UMA.

components/precache/core/precache_fetcher_unittest.cc

Index: components/precache/core/precache_fetcher_unittest.cc
diff --git a/components/precache/core/precache_fetcher_unittest.cc b/components/precache/core/precache_fetcher_unittest.cc
index f42c6c39ba1a525dba24316bbbf010103281b0c9..0549e215bcc778f3d6e824892d7c896194e0c173 100644
--- a/components/precache/core/precache_fetcher_unittest.cc
+++ b/components/precache/core/precache_fetcher_unittest.cc
@@ -1091,7 +1091,9 @@ TEST_F(PrecacheFetcherTest, MaxBytesTotal) {
   SetDefaultFlags();
   std::unique_ptr<PrecacheUnfinishedWork> unfinished_work(
       new PrecacheUnfinishedWork());
-  unfinished_work->add_top_host()->set_hostname("good-manifest.com");
+  auto* top_host = unfinished_work->add_top_host();
+  top_host->set_hostname("good-manifest.com");
+  top_host->set_visits(1);
   unfinished_work->set_start_time(base::Time::UnixEpoch().ToInternalValue());
 
   // Should be greater than kMaxParallelFetches, so that we can observe
@@ -1110,6 +1112,7 @@ TEST_F(PrecacheFetcherTest, MaxBytesTotal) {
 
   PrecacheConfigurationSettings config;
   config.set_max_bytes_total(kMaxBytesTotal);
+  config.set_global_ranking(true);
 
   factory_.SetFakeResponse(GURL(kConfigURL), config.SerializeAsString(),
                            net::HTTP_OK, net::URLRequestStatus::SUCCESS);
@@ -1117,7 +1120,9 @@ TEST_F(PrecacheFetcherTest, MaxBytesTotal) {
   PrecacheManifest good_manifest;
   for (size_t i = 0; i < kNumResources; ++i) {
     const std::string url = "http://good-manifest.com/" + std::to_string(i);
-    good_manifest.add_resource()->set_url(url);
+    auto* resource = good_manifest.add_resource();
+    resource->set_url(url);
+    resource->set_weight_ratio(static_cast<double>(i) / kNumResources);
     factory_.SetFakeResponse(GURL(url), std::string(kBytesPerResource, '.'),
                              net::HTTP_OK, net::URLRequestStatus::SUCCESS);
   }
@@ -1139,14 +1144,17 @@ TEST_F(PrecacheFetcherTest, MaxBytesTotal) {
   }
 
   // Fetcher should request config, manifest, and all but 3 resources.
-  // TODO(twifkak): I expected all but 2 resources; this result is surprising.
-  // Figure it out and explain it here.
-  EXPECT_EQ(kNumResources - 1, url_callback_.requested_urls().size());
+  EXPECT_EQ(kNumResources - 2, url_callback_.requested_urls().size());

[jamartin, 2017/02/24 21:23:29]

If it is config (1), manifest (1) and all but 3 resources (kNumResources - 3),
shouldn't you EXPECT_EQ(kNumResources - 3 + 1 + 1, ...?

[twifkak, 2017/02/25 01:13:39]

Good point. Added a comment, and clarified the math.

 
   EXPECT_TRUE(precache_delegate_.was_on_done_called());
 
   histogram.ExpectTotalCount("Precache.Fetch.PercentCompleted", 1);
   histogram.ExpectTotalCount("Precache.Fetch.TimeToComplete", 1);
+
+  const double expected_min_weight =
+      good_manifest.resource(kNumResources - 3).weight_ratio();

[jamartin, 2017/02/24 21:23:29]

good_manifest.resource.weight_ratio is the weight ratio as served from the
backend. I thought you wanted to report weight_ratio * <either the
visit-frequency of the top-host or the probability of visiting the top-host>.

[twifkak, 2017/02/25 01:13:39]

Per line 1096, top_host->visits() == 1, up until line 1139, when the std::move()
invalidates top_host. I added a `* 1` for you.

+  histogram.ExpectBucketCount("Precache.Fetch.MinWeight",
+                              1000.0 * expected_min_weight, 1);
 }
 
 // Tests the parallel fetch behaviour when more precache resource and manifest
@@ -1618,6 +1626,9 @@ TEST_F(PrecacheFetcherTest, GloballyRankResourcesAfterPauseResume) {
   // Continuing with the precache should fetch all resources, as the previous
   // run was cancelled before any finished. They should be fetched in global
   // ranking order.
+
+  base::HistogramTester histogram;
+
   {
     PrecacheFetcher precache_fetcher(
         request_context_.get(), GURL(), std::string(),
@@ -1629,6 +1640,9 @@ TEST_F(PrecacheFetcherTest, GloballyRankResourcesAfterPauseResume) {
   }
   EXPECT_EQ(expected_requested_urls, url_callback_.requested_urls());
   EXPECT_TRUE(precache_delegate_.was_on_done_called());
+
+  histogram.ExpectBucketCount("Precache.Fetch.MinWeight",
+                              1000.0 * resources.back().second, 1);
 }
 
 TEST_F(PrecacheFetcherTest, MaxTotalResources) {
@@ -1674,6 +1688,8 @@ TEST_F(PrecacheFetcherTest, MaxTotalResources) {
                            manifest.SerializeAsString(), net::HTTP_OK,
                            net::URLRequestStatus::SUCCESS);
 
+  base::HistogramTester histogram;
+
   {
     PrecacheFetcher precache_fetcher(
         request_context_.get(), GURL(), std::string(),
@@ -1685,6 +1701,11 @@ TEST_F(PrecacheFetcherTest, MaxTotalResources) {
 
   EXPECT_EQ(expected_requested_urls, url_callback_.requested_urls());
   EXPECT_TRUE(precache_delegate_.was_on_done_called());
+
+  const float expected_min_weight =
+      manifest.resource(config.total_resources_count() - 1).weight_ratio();
+  histogram.ExpectUniqueSample("Precache.Fetch.MinWeight",
+                               1000.0 * expected_min_weight, 1);
 }
 
 TEST_F(PrecacheFetcherTest, MinWeight) {